According to the prior art, automatic transmissions, particularly for motor vehicles, comprise planetary gear sets that are shifted using friction elements or shift elements such as clutches and brakes, and typically are connected to a start-up element, such as a hydrodynamic torque converter or a fluid coupling, that is subject to a slip effect and is provided optionally with a lock-up clutch.
A transmission of this type appears in EP 0 434 525 A1. It mainly comprises a drive shaft and an output shaft, which are disposed parallel to each other, a double planetary gear set disposed concentrically to the output shaft, and five shift elements in the form of three clutches and two brakes, whose selective engagement in pairs determines the different gear ratios between the drive shaft and the output shaft. The transmission has one front-mounted gear set and two power paths so that six forward gears are attained by the selective engagement of pairs of the five shift elements.
Two clutches are required in the first power path for transmitting torque from the front-mounted gear set to two elements of the double planetary gear set. They are disposed in the power flow direction substantially downstream of the front-mounted gear set in the direction of the double planetary gear set. A further clutch is provided in the second power path, which detachably connects the second power path to a further element of the double planetary gear set. The clutches are disposed in such a manner that the inner lamella carrier forms the output drive.
Furthermore, the applicant's DE 199 49 507 A1 makes known a multi-stage transmission, according to which two non-shiftable front-mounted gear sets are provided on the drive shaft and generate two rotational speeds on the output side, which, in addition to the rotational speed of the drive shaft, can be selectively meshed with a shiftable double planetary gear set acting on the output shaft by selective engagement of the shift elements such that only one of the two currently actuated shift elements must be engaged or disengaged to shift from one gear to the next higher or lower gear.
DE 199 12 480 A1 discloses an automatically shiftable motor vehicle transmission having three single-carrier planetary gear sets, as well as three brakes and two clutches, for shifting six forward gears and one reverse gear, and having a drive shaft and an output shaft. The automatically shiftable motor vehicle transmission is designed such that the drive shaft is directly connected to the sun gear of the second planetary gear set and such that the drive shaft can be connected to the sun gear of the first planetary gear set via the first clutch, and/or to the carrier of the first planetary gear set via the second clutch. Additionally or alternatively, the sun gear of the first planetary gear set can be connected to the housing of the transmission via the first brake, and/or the carrier of the first planetary gear set can be connected to the housing via the second brake, and/or to the sun gear of the third planetary gear set via the third brake to the housing.
Furthermore, DE 102 13 820 A1 makes known a multi-speed automatic transmission comprising a first input path T1 of a first transmission ratio; an input path T2 that has a higher transmission ratio than that of input path T1; a planetary gear set with four elements, namely a first element, a second element, a third element, and a fourth element in the sequence of elements in a rotational speed diagram; a clutch C-2 which transfers rotation of the input path T2 to the first element S3; a clutch C-1 which transfers rotation from the input path T2 to the fourth element S2; a clutch C-4 which transfers rotation from the input path T1 to the first element; a clutch C-3 which transfers rotation from the input path T1 to the second element C3; a brake B-1 which produces meshing of the fourth element; a brake B-2 which produces meshing of the second element; and an output element which is coupled to the third element R3.
A multi-stage transmission is described within the scope of the applicant's DE 101 15 983 A1, which has a drive shaft that is connected to a front-mounted gear set, an output shaft that is connected to a rear-mounted gear set, and a maximum of seven shift elements that can be selectively shifted to select at least seven forward gears without group shifting. The front-mounted gear set comprises a front-mounted planetary gear set or at most two non-shiftable front-mounted planetary gear sets coupled to the first -mounted planetary gear set, and the rear-mounted gear set is formed as a two-carrier, four-shaft transmission having two shiftable rear-mounted planetary gear sets, and has four free shafts. The first free shaft of this two-carrier, four-shaft transmission is connected to the first shift element, the second free shaft is connected to the second and third shift elements, the third free shaft is connected to the fourth and fifth shift elements, and the fourth free shaft is connected to the output shaft. For a multi-stage transmission, according to the invention, having a total of six shift elements, it is proposed to connect the third free shaft or the first free shaft of the rear-mounted gear set additionally to a sixth shift element. For a multi-stage transmission, according to the invention, having a total of seven shift elements, it is proposed to connect the third free shaft additionally to a sixth shift element D′ and to connect the first free shaft additionally to a seventh shift element.
Furthermore, a multi-stage transmission having at least seven gears is described within the scope of the applicant's DE 101 15 987. This transmission comprises the drive shaft and the output shaft, a non-shiftable front-mounted gear set and a shiftable rear-mounted gear set in the form of a two-carrier, four-shaft transmission. The front-mounted gear set comprises a first planetary gear set which offers, in addition to the input rotational speed of the drive shaft, a second rotational speed that can be selectively connected to a rear-mounted gear set. The rear-mounted gear set comprises two shiftable planetary gear sets which, using the six shift elements, can shift at least seven gears, wherein two power paths are formed. Advantageously, group shiftings are always avoided for every shift procedure.
Furthermore, a nine-speed multi-stage transmission is known from DE 29 36 969; it comprises eight shift elements and four gear sets, wherein one gear set serves as a front-mounted gear set, and the main gearing includes a Simpson set and a further gear set serving as the reverse gear.
Further multi-stage transmissions are known, for example, from the applicant's DE 102004040597 A1, DE 102005010210 A1 and DE 102006006637 A1.
Automatically shiftable vehicle transmissions of a planetary design have been generally described numerous times in the prior art and are continually undergoing further development and improvement. These transmissions should have a relatively simple design, in particular requiring a low number of shift elements, and avoid the need for double shifting when sequential shifting is performed, thereby ensuring that only one shift element is ever switched when shifting is performed in defined groups of gears.